The purpose of this research proposal is to determine roles of protein- tyrosine kinases (PTKs) in transduction of triggering signals induced by cross-linking of FceRI on murine mast cells. Results of this study are expected to shed light on better understanding of normal physiology of mast cells and mechanisms for allergic hypersensitivity. 1) Considering an important role of phospholipase C (PLC) in FceRI-originated signaling pathways and possible regulation of the enzyme by tyrosine phosphorylation, we shall characterize the PLC-y1-associated 44kDa protein kinase. (a) Evidence will be sought to show that this 44kDa protein is phosphorylation sites of PLC-yl in vivo an in vitro phosphorylated PLC-y1. (c) We shall antibody for isolation and cDNA cloning of the kinase. (e) The effects of genetic manipulations of the 44kDa protein-coding gene on FceRI signaling pathways will be cells. The two PTKs, termed EMb and Emt, constitute a novel subfamily of PTKs. Crosslinking of FceRI induced up-regulation of emt mRNA levels of Emt in FceRI signaling pathways. Further evidence of Emt's and Emb's roles in FceRI signaling will be sought by investigating the phosphorylation status of Emt and Emb, identifying their associated proteins, and localizing them in subcellular compartments. (b) Roles of Emb and Emt in FceRI signaling pathways will be examined through genetic manipulations and introduction of these cDNA vectors into mast cells. (c) The emb gene was reported to be defective in X-linked agammaglobulinemia (XLA). The mouse XLA model, xid, was also shown to have a point mutation in emb, resulting in the amino acid substitution Arg 28 Cys 28. Effects of this mutation on FceRI signaling pathway will be investigated using xid mouse-derived mast cells.